The present embodiments relate to transmitting a frequency-modulated signal.
In radio transmission systems, frequency modulation may be used as the modulation method. However, the carrier or carrier signals may be occasionally extinguished at the receiving antenna when transmitting data in the event of multipath propagation in the radio channel. As a result, the noise floor in the demodulated signal is increased significantly, and the transmitted signal may not be used further. Therefore, the carrier and, for example, the useful signal transmitted by the carrier may be permanently extinguished (e.g., in the case of static transmission channels in which the frequency changes slightly or does not change at all).
DE 1 230 471 B discloses the practice of erecting radio masts in an offset manner such that the dead zones occurring at particular locations as a result of multipath reception are compensated for again by the transmitted signal from another transmitter. In this case, the two transmitters transmit at the same frequency.
Transmission using pilot tones may be used in digital transmission methods (e.g., coded orthogonal frequency-division multiplexing (COFDM)). In this case, individual carriers of the multicarrier method are used as pilot tones. The pilot tones are used to estimate the channel transfer function (see Kammeyer, “Nachrichtenübertragung”, 5th edition, page 607). However, the use and evaluation of the pilot tones differ entirely from the use in analog transmission methods. In this case, a pilot tone is not used to modulate the carrier but rather for the deliberate transmission of a signal for continuous channel estimation. This signal is known to the receiver.